Positioning of mobile wireless terminal

ABSTRACT

An apparatus for determining a position of a mobile wireless station comprises means for determining the position of the mobile wireless station in accordance with a position of a first reference wireless station, a position of a second reference wireless station, a first relative angular direction between the mobile wireless station and the first reference wireless station, and a second relative angular direction between the mobile wireless station and the second reference wireless station.

This application is a divisional application of application Ser. No.10/353,002, filed Jan. 29, 2003 which is now allowed. This applicationclaims the benefit of Japanese Patent Application No. 2002-116808, filedApr. 18, 2002 in the Japanese Patent Office, the disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to positioning of a mobile wirelessterminal, and more particularly to determination of the position of amobile wireless terminal carried by a visitor in a place or facilitiesin which the visitor moves about, such as a museum or an amusement park.

2. Description of the Related Art

It is known that the position of a mobile telephone is determined by anaccess point and the determined position is sent to the telephone. In amethod used in a mobile telephone system and a PHS (Personal HandyphoneSystem), the position of a telephone is determined based on the positionof an access point which is closest to the telephone. The accuracy orresolution of the positioning is about 100 to 200 m (meters) in the PHS,and is about 800 m or more in the mobile telephone.

In another method used in the PHS, the position of a mobile telephone isdetermined by a plurality of access points in accordance with respectivelevels of RF signals received from the telephone. The positioningaccuracy is about 40 to 70 m.

It is known that the position of a mobile wireless terminal isdetermined by the triangulation method based on the propagation times ofRF signals from a plurality of access points to the terminal. Thepositioning accuracy is about 10 to 20 m.

The methods for determining a position in accordance with the levels orpropagation times of an RF signal may be effective in a small area wherethere is no obstacle. In general, however, the radio environment changeseasily due to, for example, the influence of multi-paths caused by abuilding, a wall or the like. In the methods, therefore, detected valuesexhibit wide variations depending on a device or terminal, and hence thepositioning accuracy is low.

A technique of determining the position of a mobile wireless terminal byusing the GPS (Global Positioning System) is known. In a method usingonly the GPS, the positioning accuracy is about 30 to 100 m. In anothermethod using the GPS together with an auxiliary system, a position of amobile wireless terminal estimated by the GPS is corrected in accordancewith information of the position which is measured by a referencestation. The positioning accuracy is about 5 to 50 m. In these methods,the signal processing is complex, and the accuracy may be possiblylowered at an arbitrary time in accordance with the intention of theorganization managing the GPS satellites. Inside a house or a valleybetween buildings, the positioning accuracy of the GPS is lowered.

PCT publication WO 95/04943 laid-open by Gernar on Feb. 16, 1995, whichclaims convention priority of U.S. patent Ser. No. 08/101,945 filed onAug. 4, 1993, discloses a mono-pulse azimuth radar system for trackingan automotive vehicle. In the system, the position of a precedingvehicle is determined in accordance with the distance and angle of thepreceding vehicle relative to the own vehicle. In the system, however,the position of a mobile terminal is not determined.

Japanese Patent Publication No. HEI 8-86864 (A) laid-open by Kago onApr. 2, 1996 discloses an ETC (Electronic Toll Collection) system inwhich one lane is divided into four areas, received signals from fourantennas of different directionalities are combined with one another todetect the presence or the absence of an incoming vehicle in each of theareas. In this system, in order to perform the detection athigh-accuracy in a larger range, many small areas and many antennas forthe respective areas are required.

Japanese Patent Publication No. HEI 6-222124 (A) laid-open by Tamaoki etal. on Aug. 12, 1994 discloses a technique in which a directionalantenna is used, and an actual intensity pattern of a received RF signaltransmitted from a mobile unit is matched or compared with predeterminedintensity patterns of received signals to determine the position of themobile unit. The antenna has a relatively large size, and an apparatusof a large size is necessary for controlling the directionality of theantenna.

It is an object of the invention to determine more correctly theposition of a mobile wireless terminal in a relatively narrow area.

It is another object of the invention to provide a configuration, whichis simpler in structure and smaller in size, for determining theposition of a mobile wireless terminal.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, an apparatus fordetermining a position of a mobile wireless station comprises means fordetermining the position of the mobile wireless station in accordancewith a position of a first reference wireless station, a position of asecond reference wireless station, a first relative angular directionbetween the mobile wireless station and the first reference wirelessstation, and a second relative angular direction between the mobilewireless station and the second reference wireless station.

In accordance with another aspect of the invention, an apparatus fordetermining an angular direction of a wireless station comprises meansfor determining the angular direction of the wireless station relativeto a reference angular direction, in accordance with a phase differenceassociated with a received RF signal.

In accordance with a further aspect of the invention, a wirelessapparatus comprises first and second antennas displaced from each otherby a predetermined distance for receiving an RF signal; and means fordetecting a phase difference associated with the received RF signalbetween the first and second antennas.

In accordance with a still further aspect of the invention, a program(which may be stored on a storage medium) is for use in an informationprocessing apparatus. The program is operable to effect the step ofobtaining a first relative angular direction between a mobile wirelessstation and a first reference wireless station; the step of obtaining asecond relative angular direction between the mobile wireless stationand a second reference wireless station; and the step of determining aposition of the mobile wireless station. in accordance with a positionof the first reference wireless station, a position of the secondreference wireless station, the first relative angular direction, andthe second relative angular direction.

In accordance with a still further aspect of the invention, a method fordetermining a position of a mobile wireless station comprises the stepof obtaining a first relative angular direction between the mobilewireless station and a first reference wireless station; the step ofobtaining a second relative angular direction between the mobilewireless station and a second reference wireless station; and the stepof determining a position of the mobile wireless station in accordancewith a position of the first reference wireless station, a position ofthe second reference wireless station, the first relative angulardirection, and the second relative angular direction.

According to the invention, the position of a mobile wireless terminalin a relatively narrow area can be determined more correctly, and aconfiguration, which is simpler in structure and smaller in size, fordetermining the position of a mobile wireless terminal can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic configuration of a system for determining thepositions of mobile wireless terminals in a plurality of indoor and/oroutdoor areas or facilities, such as a museum or an amusement park, inaccordance with the invention;

FIG. 2 shows a schematic configuration of another system for determiningthe positions of mobile wireless terminals in the plurality of indoorand/or outdoor areas, in accordance with the invention;

FIG. 3 shows a schematic configuration of a communication noderepresenting the reference wireless stations of FIG. 1 having at leastone antenna, and the mobile wireless terminals of FIG. 2 having at leastone antenna;

FIG. 4 shows a schematic configuration of a communication noderepresenting the mobile wireless terminals of FIG. 1 having at least twoantennas, and the reference wireless stations of FIG. 2 having at leasttwo antennas;

FIG. 5 shows a flow diagram for determining the position of the mobilewireless terminal in accordance with the source ID and the phasedifference between received RF signals;

FIGS. 6A to 6D show relationships among received data, phasedifferences, frames of angular direction data for determining theposition, and the determined position data of the mobile wirelessterminal;

FIG. 7A is useful for explaining a method for determining the positionof one mobile wireless terminal in each of the areas in the system ofFIG. 1, in accordance with the determined angular directions of therespective three reference nodes relative to the mobile wirelessterminal;

FIG. 7B is useful for explaining a method for determining the positionof one mobile wireless terminal in each of the areas in the system ofFIG. 2, in accordance with the determined angular directions of theterminal relative to the two reference nodes;

FIG. 8 is useful for explaining a technique of determining the incidentangular direction of an RF signal in accordance with the phasedifference of RF signals received by the two antennas of thecommunication node of FIG. 4;

FIG. 9 shows a block diagram of a process for determining the angulardirection of the mobile wireless terminal in accordance with thereceived RF signal;

FIG. 10 shows a block diagram of another process for determining theangular direction of the mobile wireless terminal in accordance with thereceived RF signal;

FIG. 11 shows a block diagram of a further process for determining theangular direction of a mobile wireless terminal in accordance with thereceived RF signal;

FIG. 12 shows a block diagram of a logic process for determining thedirection of a mobile wireless terminal in accordance with the receivedRF signal;

FIGS. 13A to 13C show logic levels of different signals of FIG. 12 fordetermining the absolute phase difference;

FIGS. 14A and 14B show logic levels of different signals of FIG. 12 fordetermining the sign of the phase difference;

FIGS. 15A and 15B are useful for explaining different methods fordetermining the position of the terminal by using a plurality ofreference communication nodes;

FIG. 16 shows an example of the arrangement of two antennas in themobile wireless terminal in FIG. 1;

FIGS. 17A and 17B show another example of the arrangement of twoantennas in the mobile wireless terminal in FIG. 1, and an intensitypattern of a received RF signal of this example, respectively; and

FIG. 18 shows an arrangement which includes a switch for correcting anerror due to such a path difference.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic configuration of a system for determining thepositions of mobile wireless terminals or stations 260 and 280 carriedby the visitors in a plurality of indoor and/or outdoor areas 62 and 64and the like, in a place or facilities, such as a museum or an amusementpark, where visitors move about, in accordance with the invention. Aserver 110 which provides information to mobile wireless terminals inthe areas and collects information from the terminals, a positiondetermining apparatus 120 which determines the position of a mobilewireless terminal in each area, and an access point 200 which is fixedin position are connected to one another via a wired local area network(LAN) 50. The access point 200 serves also as a reference wirelessstation which is used as a position reference. The server 110, theposition determining apparatus 120, the access point 200 and the likemay be geographically separated from one another, and connected to oneanother via a public switched telephone network (PSTN), leased lines orthe like.

The server 110 has a processor 112 and a storage device 114. Theprocessor 112 operates in accordance with an application program for theserver function stored in the storage device 114. Alternatively, theserver function may be implemented on the processor 112 in the form ofhardware. The position determining apparatus 120 has a processor 122 anda storage device 124. The processor 122 operates in accordance with anapplication program for the position determining function stored in thestorage device 124. Alternatively, the position determining function maybe implemented on the processor 122 in the form of hardware. Theposition determining apparatus 120 may be eliminated, and the positiondetermining function may be implemented by another apparatus, such asthe server 110, the access point, or another reference wireless stationor mobile wireless terminal as described later.

The visitors who carry the respective mobile wireless terminals 260 and280 and the like enter the areas 62 and 64 which are indoor and/oroutdoor, move in the areas, and then go out of the areas. Thus, themobile wireless terminals 260 and 280 move around in indoor and/oroutdoor areas including the areas 62 and 64. Each of the mobile wirelessterminals 260 and 280 communicates with the server 110 via the accesspoint 200 to receive suitable guidance information for the currentposition of the terminal from the server 110, and presents theinformation visually or audibly.

The access point 200, and reference wireless stations 220, 230 and 240cover the areas 62 and 64. The reference wireless stations 220, 230 and240 may communicate in the wireless form with the access point 200 tocommunicate with one another via the access point 200. Alternatively,the reference wireless stations 220, 230 and 240 may be connected via acable to the LAN 50. It is assumed that, in the place or the facilities,the positions A (x₁,y₁), B (x₂,y₂), C (x₃,y₃) and D (x₄,y₄) of thereference wireless stations 200, 220, 230 and 240 are known. Preferably,the positions of the reference wireless stations 220, 230 and 240 arefixed. The reference wireless station may be moved to a differentposition, while the motion of the reference wireless station does notaffect the positioning.

Each of the reference wireless stations 200, 220, 230 and 240 has atleast one antenna for positioning. Each of the mobile wireless terminals260 and 280 has at least two antennas for positioning. The referencewireless stations 200, 220, 230 and 240, and the mobile wirelessterminals 260 and 280 serve as communication nodes. Each of thereference wireless stations 200, 220, 230 and 240 transmits an RF signalfor determining the position (x,y) of each of the mobile wirelessterminals 260 and 280. The position (x,y) of each of the mobile wirelessterminals 260 and 280 is determined or detected in accordance with theRF signals received by the mobile wireless terminal as described later.

FIG. 2 shows a schematic configuration of another system for determiningthe positions of mobile wireless terminals 262 and 282 in the pluralityof indoor and/or outdoor areas 62 and 64 and the like, which is amodification of the system of FIG. 1, in accordance with the invention.The server 110, the position determining apparatus 120, and an accesspoint 202 which is fixed in position are connected to one another viathe wired LAN 50. The access point 202 serves also as a referencewireless station.

The mobile wireless terminals 262 and 282 move around in indoor and/oroutdoor areas including the areas 62 and 64. Each of the mobile wirelessterminals 262 and 282 communicates with the server 110 via the accesspoint 202 to receive suitable guidance information for the currentposition of the terminal from the server 110, and presents theinformation visually or audibly.

The access point 202, and reference wireless stations 222, 232 and 242cover the areas 62 and 64. The reference wireless stations 222, 232 and242 communicate in the wireless form with the access point 202 tocommunicate with one another via the access point 202. Alternatively,the reference wireless stations 222, 232 and 242 may be connected via acable to the LAN 50. It is assumed that, in the place or the facilities,the positions A, B, C and D of the reference wireless stations 202, 222,232 and 242 are known. Preferably, the positions of the referencewireless stations 222, 232 and 242 are fixed. The reference wirelessstation may be moved to a different position, while the motion of thereference wireless station does not affect the positioning.

Each of the reference wireless stations 202, 222, 232 and 242 has atleast two antennas for positioning. Each of the mobile wirelessterminals 262 and 282 has at least one antenna for positioning. Thereference wireless stations 202, 222, 232 and 242, and the mobilewireless terminals 262 and 282 serve as communication nodes. Each of themobile wireless terminals 262 and 282 transmits an RF signal fordetermining the position (x,y) of the terminal, to the referencewireless stations 202, 222, 232 and 242. The position (x,y) of theterminal is determined or detected in accordance with the RF signalsreceived by the reference wireless stations 202, 222, 232 and 242, asdescribed later.

FIG. 3 shows a schematic configuration of a communication node 300representing the reference wireless stations 200, 220, 230 and 240 ofFIG. 1 having at least one antenna, and the mobile wireless terminals262 and 282 of FIG. 2 having at least one antenna. The node 300 has anantenna 351, a frequency converter 353 coupled to the antenna 351, amodem 355 coupled to the frequency converter 353, a signal processor 370coupled to the modem 355, and a memory 372 including a ROM, a RAM andthe like. The memory 372 stores programs and data for the processor 370.

The signal processor 370 of the access point 200 of FIG. 1 is connectedto the LAN 50. The signal processors 370 of the reference wirelessstations 220, 230 and 240 may communicate in the wireless form with thesignal processor 370 of the access point 200 to communicate with oneanother via the access point 200. Alternatively, the signal processor370 of each of the reference wireless stations 220, 230 and 240 may beconnected via a cable to the LAN 50. The signal processor 370 of each ofthe mobile stations 262 and 282 of FIG. 2 communicates in the wirelessform with the access point 202.

The signal processor 370 provides transmitted data and control signalsfor communication to the modem 355, and receives received data andcontrol signals for communication from the modem. The control signalsmay be transmitted to or received from the server 110 or the positiondetermining apparatus 120 via the signal processor 370. The transmitteddata contains a source identifier (ID). A carrier signal modulated withthe transmitted data by the modem 355 is upconverted by the frequencyconverter 353 and then transmitted as an RF signal via the antenna 351.On the other hand, an RF signal received by the antenna 351 isdownconverted to an intermediate frequency (IF) signal by the frequencyconverter 353, which is then provided to the modem 355. Thedownconverted signal is demodulated by the modem 355 to produce receiveddata and the received data is provided to the signal processor 370.

FIG. 4 shows a schematic configuration of a communication node 400representing the mobile wireless terminals 260 and 280 of FIG. 1 havingat least two antennas, and the reference wireless stations 202, 222, 232and 242 of FIG. 2 having at least two antennas. The node 400 has twoantennas 411 and 451, frequency converters 413 and 453 coupled to therespective antennas 411 and 451, respectively, a phase differencedetector 415 coupled to the frequency converters 413 and 453, a modem455 coupled to the frequency converters 413 and 453, an ID detector 457coupled to the modem 455, a signal processor 470, and a memory 472including a ROM, a RAM and the like. The signal processor 470 is coupledto the phase difference detector 415, the modem 455 and the ID detector457. The memory 472 stores programs and data for the processor 470.Alternatively, the ID detector 457 may be eliminated, and the IDdetecting function of the ID detector 457 may be implemented on theprocessor 470.

The signal processor 470 of each of the mobile stations 260 and 280 ofFIG. 1 communicates in the wireless form with the access point 200. Thesignal processors 470 of the reference wireless stations 222, 232 and242 of FIG. 2 communicate in the wireless form with the signal processor470 of the access point 202 to communicate with one another via theaccess point 202. Alternatively, the signal processor 470 of each of thereference wireless stations 222, 232 and 242 may be connected via acable to the LAN 50.

For positioning, the node 400 of FIG. 4 receives the RF signaltransmitted from the node 300 of FIG. 3, via the antennas 411 and 451.Each of the mobile wireless terminals 260 and 280 of FIG. 1 serving asthe node 400 receives different transmitted RF signals from thereference wireless stations 220, 230 and 240 of FIG. 1 serving as thenode 300. Each of the reference wireless stations 222, 232 and 242 ofFIG. 2 serving as the node 400 receives different transmitted RF signalsfrom the mobile wireless terminals 262 and 282 of FIG. 2 serving as thenode 300.

Transmitted data, which is produced by the signal processor 470, isprovided to the modem 455. A carrier signal modulated with thetransmitted data by the modem 455 is upconverted by the frequencyconverter 413 or 453 and then transmitted as an RF signal to the node300 via the antenna 411 or 451.

The RF signals from the node 300, which are received via the antennas411 and 451, are downconverted to IF signals by the respective frequencyconverters 413 and 453. Both of the downconverted signals are providedto the phase difference detector 415. Alternatively, both of thereceived RF signals, which have not yet been downcoverted in therespective frequency converters 413 and 453, may be provided to thephase difference detector 415. One or both of the downconverted signalsfrom the frequency converters 413 and 453 are provided also to the modem455. When both of the signals are provided to the modem 455, receiveddata on one of the signals are selected by the modem 455, or both thesignals are combined with each other for demodulation in a goodcondition.

FIG. 5 shows a flow diagram of a process for determining the position ofa mobile wireless terminal in accordance with the source ID detected bythe ID detector 457 and with the phase difference between received RFsignals detected by the phase difference detector 415 of the node 400.The position is determined by the processor 122, 112, 470 or 370 of theposition determining apparatus 120, the server 110, the node 400 or thenode 300, in accordance with a program stored in the correspondingstorage device 124, 114, 472 or 372.

At Step 501 of FIG. 5, the processor 122, 112, 470 or 370 obtains thesource ID and the phase difference between received RF signals. At Step503, the processor derives, from the source ID and the phase difference,a relative angular direction between the mobile wireless terminal andthe reference node. At Step 505, the processor determines the positionof the mobile wireless terminal in accordance with the known position ofthe reference node, the source ID, and the relative angular direction.

FIGS. 6A to 6D show relationships among received data DATA₁, DATA₂ andDATA₃ demodulated by the modem 455, phase differences (PDs), Δφ₁, Δφ₂and Δφ₃, detected by the phase difference detector 415, frames ofangular direction data for determining the position, and the determinedposition data (x,y) of a mobile wireless terminal ID_(T1).

Referring also to FIG. 4, the received data DATA₁, DATA₂ and DATA₃ ofFIG. 6A which are produced by the modem 455 are provided to the signalprocessor 470. The received data from each node 300 contains the sourceID of the node 300. The received data DATA₁, DATA₂ and DATA₃ containrespective source IDs, ID₁, ID₂ and ID₃, of the reference wirelessstations 200, 220, 230 and 240 of FIG. 1, or the mobile wirelessterminals 262 and 282 and the like of FIG. 2. The received sets of data,DATA₁, DATA₂ and DATA₃, are provided also to the ID detector 457. The IDdetector 457 detects and extracts the source IDs, ID₁, ID₂ and ID₃, inthe received data to provide the extracted IDs to the signal processor470. The phase differences PDs, Δφ₁, Δφ₂ and Δφ₃, of FIG. 6B detected bythe phase difference detector 415, as described later, are provided tothe signal processor 470.

The signal processor 470 of the communication node 400 determines theangular directions of the mobile wireless terminals 260 and 280 inaccordance with the phase differences PDs, combines the determinedangular directions with the source IDs to send the determined angulardirections combined with the source IDs to another node or apparatus.The calculation of the angular direction in accordance with the phasedifference may be performed by the phase difference detector 415, in themanner described later. As shown in FIG. 6D, the position (x, y) of themobile wireless terminal (ID_(T1)) is determined in accordance with theframes of the sets of the source ID and the angular direction shown inFIG. 6C, in the manner described later. The sets of the source ID andthe angular direction, (ID₁, θ₁), (ID₂, θ₂) and (ID₃, θ₃), are sent toanother apparatus, preferably, the position determining apparatus 120 inorder to determine the position of the mobile wireless terminal shown inFIG. 6D. The determined position may be sent to the mobile wirelessterminal for use in the terminal. Alternatively, in the mobile wirelessterminal 260 or 280 of FIG. 1, the position of the terminal may bedetermined by the own signal processor 470 without sending the angulardirection sets to another apparatus.

As described above, the signal processor 470 of the node 400 may sendthe frames of the source ID and the angular direction shown in FIG. 6C,to the other node, and the position shown in FIG. 6D may be determinedby the other node or apparatus. For example, the signal processor 470may send the frames to the position determining apparatus 120 via theaccess point 200 or 202 and the LAN 50, and the position determiningapparatus 120 may determine the position in accordance with the frames.For example, the signal processor 470 may send the frames to the server110 via the access point 200 or 202 and the LAN 50, and the server 110may determine the position in accordance with the received frames. Forexample, the signal processor 470 may send the frames to the onecommunication node 300, and the signal processor 370 of thecommunication node 300 may determine the position in accordance with thereceived frames. For example, the signal processor 370 or 470 of theaccess point 200 or 202 may collect the frames from the other nodes anddetermine the position in accordance with the received frames. When theposition determination is performed by an apparatus other than themobile wireless terminals 240, 260, 242 and 262, the processing load inthe terminals can be reduced.

Alternatively, the signal processor 470 of the node 400 may produceframes (not shown) including respective sets of the source ID and thephase difference PD, (ID₁, θ₁), (ID₂, θ₂) and (ID₃, θ₃), and send theframes to another node. The angular direction and the position aredetermined by the other node or apparatus in accordance with the sourceID and the phase difference PD.

The communication between the reference wireless station and the mobilewireless terminal, and hence communication units of the nodes 300 and400 operate in accordance with, typically, a short distance wirelesscommunication standard such as the Bluetooth standard or a wireless LANstandard. The Bluetooth standard uses the 2.4 GHz band (2.402 GHz-2.480GHz) called ISM (Industrial, Scientific and Medial) band. It definesthree power classes 1 to 3 for 1 mW, 2.5 mW and 100 mW. In Power Classes1 to 3, short distance communications in a range of about 10 m to about100 m can be done. The Bluetooth employs the GFSK modulation and thefrequency hopping scheme. The wireless LAN standard, such as IEEE802.11, uses the 2.4 GHz band (2.40 GHz-2.497 GHz) and employs thespread spectrum scheme and the DBPSK or DQPSK modulation, or thefrequency hopping scheme and the GFSK modulation, for communications.

FIG. 7A is useful for explaining a method for determining the position(x, y) of one mobile wireless terminal T in each of the areas in thesystem of FIG. 1, in accordance with the determined angular directionsθ₁, θ₂ and θ₃ of the respective three reference nodes or referencewireless stations A, B and C relative to the mobile wireless terminal T.For that purpose, it is assumed that the positions of the threereference nodes A, B and C are known.

In FIG. 7A, it is assumed that the mobile wireless terminal T has areference angular direction, i.e. reference direction of the angle, orazimuth RT which is determined as described later. The determinedangular directions between the reference direction RT in the mobilewireless terminal T and the three reference nodes A, B and C areindicated by θ₁, θ₂ and θ₃, respectively. The three referencecommunication nodes A, B and C are three ones of the reference wirelessstations 200 to 240 of FIG. 1. When the three reference nodes A, B and Care placed so that a straight line connecting the positions of thereference nodes A and B, and a straight line connecting the positions ofthe reference nodes B and C lie outside the area, the position of themobile wireless terminal T can be uniquely determined in accordance withthe determined angular directions θ₁, θ₂ and θ₃ because the positions ofthe reference nodes A, B and C are known.

When the reference angular direction RT is adapted by any means toconstantly indicate geographically the same azimuth and the tworeference nodes A and B are placed so that the straight line connectingthe positions of the two reference nodes A and B lies outside the area,the position of the mobile wireless terminal T can be uniquelydetermined in accordance with the angular directions of the tworeference nodes relative to the reference direction RT in the mobilewireless terminal T. for example, the angular directions θ₁ and θ₂ ofthe nodes A and B.

FIG. 7B is useful for explaining a method for determining the position(x, y) of one mobile wireless terminal T in each of the areas in thesystem of FIG. 2, in accordance with the determined angular directionsθ₁ and θ₂ of the mobile wireless terminal T relative to the tworeference nodes A and B in the system. The position of the mobilewireless terminal T is determined in accordance with at least twodetermined angular directions of the mobile wireless terminal T It isassumed that the positions of the two reference nodes A and B are known.

In FIG. 7B, it is assumed that the two reference communication nodes Aand B have reference angular directions R_(A) and R_(B), respectively.It is assumed that the determined angular directions between the mobilewireless terminal T and the reference directions R_(A) and R_(B) in thetwo reference communication nodes A and B are indicated by θ₁ and θ₂,respectively. The two reference communication nodes A and B are two onesof the reference wireless stations 202 to 242 of FIG. 2.

When the reference angular directions R_(A) and R_(B) of the tworeference communication nodes A and B are determined independently ofeach other, an angular direction θ₁₂ between the reference directionR_(A) in the one reference communication node A and the other node B,and an angular direction θ₂₁ between the reference direction R_(B) inthe other reference communication node B and the one node A aredetermined, and the position of the mobile wireless terminal T can beuniquely determined in accordance with the known positions of the tworeference communication nodes A and B, and with the determined angulardirections, θ₁₂, θ₂₁, θ₁ and θ₂, i.e. (θ₁₂-θ₁) and (θ₂₁-θ₂). In order todetermine the angular directions θ₁₂ and θ₂₁, each of the referencecommunication nodes A and B in the form of the node 400 of FIG. 4receives an RF signal which contains the source ID, which is transmittedfrom the other reference communication node (400) B or A via the antenna411 or 451 of the one node, and which is similar to the RF signal fromthe node 300 of FIG. 3.

On the other hand, when the relationship between the reference angulardirections or azimuths R_(A) and R_(B) in the positions of the tworeference communication nodes A and B is known and the reference nodes Aand B are placed so that the straight line connecting the positions ofthe two reference nodes A and B lies outside the area, the position ofthe mobile wireless terminal T can be uniquely determined in accordancewith the known positions of the two reference communication nodes A andB and with the determined angular directions θ₁ and θ₂ relative to thereference directions R_(A) and R_(B).

FIG. 8 is useful for explaining a technique of determining the incidentangular direction of an RF signal in accordance with the phasedifference of RF signals received by the two antennas ANT1 (411) andANT2 (451) of the communication node 400 of FIG. 4, or of IF signals onthe RF signals. An RF signal at, for example, a frequency in thevicinity of 2.5 GHz has a wavelength X of about 12 cm. The antennas ANT1and ANT2 are on a horizontal line and displaced from each other by adistance d (<λ/2) of, for example, about 3 cm. A straight line passingthe positions of the antennas ANT1 and ANT2 is defined as the antennareference line. A direction on a horizontal plane perpendicular to theantenna reference line is defined as a reference angular direction R ofthe communication node 400. It is advantageous to use the referencedirection R as the reference directions R_(T), R_(A) and R_(B) in FIGS.7A and 7B.

Referring to FIG. 8, when an RF signal, which horizontally enters at anangle θ relative to the reference direction R, is received by theantennas ANT1 and ANT2, the path difference is d·sin θ. The phasedifference between the two antennas ANT1 and ANT2 is Δφ=2π(d·sin θ)/λ.Therefore, the incident angular direction of the RF signal relative tothe reference direction R is θ=Sin⁻¹ ((λ./2π d) Δφ).

When the reference angular direction R_(T) of the mobile wirelessterminal T, as described in connection with FIG. 7A, is adapted toconstantly indicate geographically the same azimuth, for example, thedirection of the N-pole, the determined values of the angular directionscan be corrected by the difference of the reference angular direction Rof FIG. 8 relative to the reference angular direction R_(T) which isdetermined by using a gyroscope, a compass or the like that can beprovided in the mobile wireless terminal T.

FIG. 9 shows a block diagram of a process for determining the angulardirection θ of the mobile wireless terminal in accordance with thereceived RF signal. FIG. 9 can be seen as a flowchart of the process fordetermining the direction. An RF signal, which is received by theantenna ANT1 411, is downconverted by the frequency converter 413 toproduce an IF signal A₁ cos(ω+φ₁), where A₁ indicates the amplitude, ωindicates the angular velocity, and φ₁ indicates the initial angularphase. An RF signal, which is received by the antenna ANT2 451, isdownconverted by the frequency converter 453 to produce an IF signal A₂cos(ωt+φ₂), where A₂ indicates the amplitude, ω indicates the angularvelocity, and φ₂ indicates the initial angular phase. The IF signalshave a frequency of, for example, 50 MHz. Alternatively, as describedabove, the signals A₁ cos(ωt+φ₁) and A₂ cos(ωt+φ₂) may be RF signalswhich have not yet been downcoverted. The signals A₁ cos(ωt+φ₁) and A₂cos(φt+φ₂) are provided to the phase difference detector 415.

In the phase difference detector 415, the signals A₁ cos(ωt+φ₁) and A₂cos(φt+φ₂) are corrected in amplitude by amplitude correctors 417 and457, each of which is configured by a limiting amplifier, to benormalized, to thereby produce normalized signals cos (ωt+φ₁) and cos(ωt+φ₂)

Both of the normalized signals cos(ωt+φ₁) and cos(ωt+φ₂) are provided toan adder 419 and to a subtracter 459. The adder 419 produces a sum ofthe signals, cos(ωt+φ₁)+cos(ωt+φ₂)=cos((ω₁−φ₂)/2)·cos(ωt+(φ₁+φ₂)/2). Thesubtracter 459 produces a signal representing the difference between thesignals, cos(ωt+φ₁)−cos(ωt+φ₂)=−sin((+φ₂)/2)·sin(ωt+(φt+(φ₁+φ₂)/2).

The sum and difference signals are squared by square-law detectors 422and 462, respectively, and the level or magnitude of a square of thesum, cos²((φ₁−φ₂)/2), and that of a square of the difference,sin²((φ₁−φ₂)/2), are determined in respective level detectors 424 and464. The levels are provided to a divider 426. In the divider 426, sin²((φ₁−φ₂)/2)/cos²((φ₁−φ₂)/2)tan²((φ₁−φ₂)−/2) is determined in accordancewith the levels to produce a square root of the value,|tan((φ₁−φ₂)/2)|=tan(|φ₁−φ₂|/2), and produce the absolute value of thephase difference |Aφ|=|φ₁−φ₂|. The absolute value of the phasedifference |Δφ| is provided to an incident direction determining device480. Preferably, each of the level detectors 424 and 464 includes an A/Dconverter and provides a digital signal as an output.

On the other hand, the sum signal is provided also to an amplitudecorrector 434 configured by a limiting amplifier, to be corrected inamplitude and normalized, to thereby produce a signalcos(ωt+(φ₁+φ₂)/2)). The difference signal is delayed by π/2 in a delayelement 432 to produce a signal sin((φ₁−φ₂)/2)cos(ωt+(φ₁+φ₂)/2). Thedelayed signal is provided to an amplitude corrector 435 configured by alimiting amplifier, to be corrected in amplitude and normalized, tothereby produce a signal sgn(+1−φ₂)·cos(ωt+(φ₁+φ₂)/2), where sgn(x)=+1for x>0, and sgn(x)=1 for x<0.

The signal cos(ωt+(φ₁+φ₂)/2) from the amplitude corrector 434 is addedto the signal sgn (φ₁−φ₂) cos(ωt+(φ₁+φ₂)/2) from the amplitude corrector435 in an adder 442. The adder 442 produces a value of two (2) for thephase difference φ₁−φ₂>0 (zero), i.e. positive, and the adder produces avalue of zero (0) for the phase difference φ₁−φ₂<0 (zero), i.e.negative. The output of the adder 442 is thresholded by a signdetermining device 444 to determine the value as either positive (+) ornegative (−). The positive/negative sign is provided as the sign of thephase difference (φ₁−φ₂) to the incident direction determining device480.

In the manner described in connection with FIG. 8, the incidentdirection determining device 480 determines the incident angulardirection θ of the RF signal in accordance with the absolute phasedifference |Δ|φ₁−φ₂|, the sign (+ or −) of the phase difference, and thedistance d between the antennas.

Alternatively, the function for determining the incident angulardirection in the incident direction determining device 480, or fordetermining the incident angular direction in the divider 426 and theincident direction determining device 480 may be performed by the signalprocessor 470 of the node 400, another node, another apparatus or thelike rather than the phase difference detector 415. When the function isperformed in another node or apparatus, the level signals which areprovided from the level detectors 424 and 464 in FIG. 9 to the divider426, and the sign signal which is provided from the sign judgementdevice 444 to the incident direction determining device 480 may be sentin combination with the source ID to the other node or apparatus, and,for example, to the position determining apparatus 120 via the accesspoint 200 or 202 and the LAN 50.

FIG. 10 shows a block diagram of another process for determining theangular direction 0 of the mobile wireless terminal in accordance withthe received RF signal, which is a modification of the process of theblock diagram of FIG. 9. FIG. 10 also can be seen as a flowchart of theprocess for determining the direction. In the process of FIG. 10, inplace of the divider 426 and the incident direction determining device480 of FIG. 9, a ROM table 482 for determining the incident direction,or a processor 482 including such a ROM table is provided. The ROM table482 uses, as indices, both of the levels of a square of the sum,cos²(φ₁−φ₂)/2), and a square of the difference, sin²((φ₁−φ₂)/2), fromthe respective level detectors 424 and 464, and the sign from the signdetermining device 444, to provide, as an output, the value of thecorresponding incident angle θ of the RF signal. In the ROM table 482, atable is provided which correlates the indices with the value of theincident direction θ in accordance with the equations which have beendescribed in connection with FIG. 8.

FIG. 11 shows a block diagram of a further process for determining theangular direction θ of a mobile wireless terminal in accordance with thereceived RF signal, which is a modification of the process of the blockdiagram of FIG. 10. FIG. 11 also can be seen as a flowchart of theprocess for determining the direction. In the process of FIG. 11, inplace of the square-law detectors 422 and 462 and the level detectors424 and 464 of FIG. 10, a square-law detector 423 and a level detector425 are connected between switches 420 and 430. The switch 420 isswitched in synchronization by a switching control signal to alternatelyprovide the sum cos((φ₁−φ₂)/2)cos(ωt+(φ₁−φ₂)/2) from the adder 419 andthe difference −sin((φ₁−φ₂)/2)sin((ωt+(φ₁−φ₂)/2) from the subtracter 459to the square-law detector 423 and the level detector 425. The switch430 alternately provides the level of a square of the sum,cos²((φ₁−φ₂)/2), and the level of a square of the difference,sin²((φ₁−φ₂)/2), to the ROM table 482. In the same manner as the tabledescribed above, the ROM table 482 provides, as an output, the value ofthe corresponding incident angular direction θ of the RF signal.

In FIGS. 10 and 11, alternatively, the ROM table 482 may be provided inthe signal processor 470 of the node 400, another node, anotherapparatus or the like rather than the phase difference detector 415, todetermine the incident angular direction. When the incident angulardirection is determined in another node or apparatus, the level signalsprovided from the level detectors 424 and 464 or from the level detector425 via the switch 430 to the ROM table 482, and the sign signalprovided from the sign determining device 444 to the ROM table 482 maybe sent in combination with the source ID to the other node orapparatus, and, for example, to the position determining apparatus 120via the access point 200 or 202 and the LAN 50.

FIG. 12 shows a block diagram of a logic process for determining thedirection of a mobile wireless terminal in accordance with the receivedRF signal, as an alternative to the processes of FIGS. 9 to 11. FIG. 12also can be seen as a flowchart of the process for determining thedirection.

FIGS. 13A to 13C show logic levels of different signals of FIG. 12 fordetermining the absolute phase difference. FIGS. 14A and 14B show logiclevels of different signals of FIG. 12 for determining the sign of thephase difference.

Referring to FIG. 12, the signal from the frequency converter 413 ofFIG. 4 is provided to a binarizing element 467, and thresholded in thebinarizing element 467 to produce a binary signal A. The signal outputfrom the frequency converter 453 of FIG. 4 is provided to a binarizingelement 477, and thresholded in the binarizing element 477 to produce abinary signal B.

The signal A from the binarizing element 467 is provided to one input ofan exclusive OR (EXOR) gate 469, and the signal B of the binarizingelement 477 is provided to the other input of the exclusive OR (EXOR)gate 469. The EXOR gate 469 EXORs the signal A with the signal B toprovide an EXOR output. FIGS. 13A and 13B show relationships amongsignals when the signal A is advanced in phase from the signal B. FIG.13C shows relationships among signals when the signal A is delayed inphase from the signal B. As shown in FIGS. 13A to 13C, as the absolutephase difference |Δφ| between the signals A and B becomes larger, thepulse width of the EXOR output becomes larger. The pulse width of theEXOR output indicates the absolute phase difference.

The output from the EXOR gate 469 is provided to a low-pass filter (LPF)472, and filtered by the LPF 472 to convert the phase difference into ananalog level. The analog level of the analog signal output from the LPF472 is detected as a digital value by a level detector 474 to producethe absolute phase difference |Δφ|=φ₁−φ₂|. The absolute phase difference|Δφ| is provided to an incident direction determining device 486.

Referring to FIG. 12, the signal B from the binarizing element 477 isprovided also to a latch element 437. In the latch element 437, thesignal B is latched at a rising edge of the signal A of the binarizingelement 467.

As shown in FIG. 14A, when the signal A is advanced in phase from thesignal B, an output of the latch element 437 is always at the Low (L)level. As shown in FIG. 14B, when the signal A is delayed in phase fromthe signal B, the output from the latch element 437 is always at theHigh (H) level. The signal, indicating the H or L level, from the latchelement 437 is provided to a sign determining device 445. When thesignal is at the H level, the sign determining device 445 provides thesign of positive (+) to the incident direction determining device 486,and, when the signal is at the L level, the sign determining deviceprovides the sign of negative (−) to the incident direction determiningdevice 486.

In the manner described in connection with FIG. 8, the incidentdirection determining device 486 determines the incident angulardirection θ of the RF signal in accordance with the absolute phasedifference |Δφ|=|φ₁−φ₂|, the sign (+ or −) of the phase difference, andthe distance d between the antennas. The incident direction determiningdevice 486 may include a ROM table, which is similar to that shown inFIG. 10, and in which the absolute phase difference and the sign areused as indices.

Alternatively, the function for determining the incident angulardirection in the incident direction determining device 486 may beperformed by the signal processor 470 of the node 400, another node,another apparatus or the like rather than the phase difference detector415. When the function is performed in another node or apparatus, thelevel signal provided from the level detector 474 in FIG. 12 to theincident direction determining device 486, and the sign signal providedfrom the sign judgement device 445 to the incident direction determiningdevice 486 may be sent in combination with the source ID to the othernode or apparatus, and, for example, the position determining apparatus120 via the access point 200 or 202 and the LAN 50.

FIGS. 15A and 15B are useful for explaining different methods fordetermining the position of a terminal by using a plurality of referencecommunication nodes. In FIGS. 15A and 15B, it is assumed that adetermined angle between an angular direction D_(A) of the terminal Trelative to the reference node A and an angular direction D_(B) of theterminal T relative to the reference node B is θ_(AB), a determinedangle between the angular direction D_(B) of the terminal T relative tothe reference node B and an angular direction D_(C) of the terminal Trelative to the reference node C is θ_(BC), and an determined anglebetween the angular direction D_(C) of the terminal T relative to thereference node C and the angular direction D_(A) of the terminal Trelative to the reference node A is θ_(CA).

The position determining apparatus 120 of FIGS. 1 and 2, the server 110of FIGS. 1 and 2, the signal processor 470 of the node 400 of FIG. 4, orthe signal processor 370 of the node 300 of FIG. 3 obtains the sets ofthe source ID and the angular direction, (ID₁,θ₁), (ID₂,θ₂) and(ID₃,θ₃), to determine the position (x,y) of the terminal T as describedabove.

From FIG. 7A, it is seen that, when the system of FIG. 1 determines theposition of a mobile wireless terminal by using more than threereference wireless stations, different terminal positions may beobtained for different combinations of the reference wireless stationsdue to measurement errors of angular directions. From FIG. 7B, it willbe seen that, when the system of FIG. 2 determines the position of amobile wireless terminal by using more than two reference wirelessstations, different terminal positions may be obtained for differentcombinations of the reference wireless stations due to a measurementerror of angular directions.

Referring to FIG. 15A, when a provisional position of the terminal Twhich is determined in accordance with the angular direction D_(A) ofthe terminal T relative to the reference node A and the angulardirection D_(B) of the terminal T relative to the reference node B, witha provisional position of the terminal T determined in accordance withthe angular direction D_(B) of the terminal T relative to the referencenode B and the angular direction D_(C) of the terminal T relative to thereference node C, and with a provisional position of the terminal Tdetermined in accordance with the angular direction D_(C) of theterminal T relative to the reference node C and the angular directionD_(A) of the terminal T relative to the reference node A do not coincidewith each other, the position determining apparatus 120, the server 110,or the signal processor 470 or 370 determines the average of thedetermined provisional positions in an orthogonal coordinate system(x,y) as an appropriate position of the terminal T. Alternatively, thecenter of gravity of a polygon in which the vertexes lie respectively onthe provisional positions may be determined as an appropriate positionof the terminal T.

Referring to FIG. 15B, when a provisional position of the terminal Tdetermined in accordance with the angular direction D_(A) and theangular direction D_(B), a provisional position of the terminal Tdetermined in accordance with the angular direction D_(B) and theangular directions D_(C), and a provisional position of the terminal Tdetermined in accordance with the angular direction D_(C) and theangular direction D_(A) do not coincide with each other, a provisionalposition which has an angle closest to a right angle (90) among thedetermined angles θ_(AB), θ_(BC) and θ_(CA) is determined or selected asan appropriate position of the terminal T. Alternatively, several angleswhich are closest to a right angle are extracted from the angles θ_(AB),θ_(BC) and θ_(CA), and the average of the provisional positions havingthe extracted angles may be determined as an appropriate position of theterminal T. Alternatively, angles which are in a range of 45 to 135degrees are extracted from the angles, and the average of theprovisional positions with the extracted angles may be determined as anappropriate position of the terminal T

FIG. 16 shows an example of the arrangement of two antennas a₁ and a₂ ineach of the mobile wireless terminals 260 and 280 in FIG. 1. Referringto FIG. 16, the antennas a₁ and a₂ are placed on or near the uppersurface of the mobile wireless terminal 260 or 280 and displaced fromeach other by a distance d. Preferably, each of the antennas a₁ and a₂is a chip or planar antenna having one side edge of about 1 cm or less.The intensity pattern of the received and transmitted RF signals for theantennas a₁ and a₂ is substantially uniform in all of the horizontaldirections, and the antennas a₁ and a₂ can receive an RF signal radiatedfrom an antenna of a reference node in an arbitrary direction.Preferably, the antennas a₁ and a₂ are placed inside the terminal, andare not required to be exposed to the outside.

FIGS. 17A and 17B show another example of the arrangement of twoantennas in the mobile wireless terminal 260 or 280 in FIG. 1, and anintensity pattern of the received RF signal of this example,respectively. Referring to FIG. 17A, a pair of antennas a₁₁ and a₁₂ areplaced on or near the front surface of the mobile wireless terminal 260or 280 and displaced from each other by a distance d. Another pair ofantennas a₂₁ and a₂₂ are placed on or near the back surface of themobile wireless terminal 260 or 280 and displaced from each other by thedistance d. Preferably, each of the antennas a₁₁, a₁₂, a₂₁l and a₂₂ is achip or planar antenna having one side edge of about 1 cm or less. Thepair of antennas a₁₁ and a₁₂ exhibit higher directionality in a half ofthe air space outside the terminal in front of the associated surface,and the received and transmitted RF signal intensity pattern exhibitshigher intensity in the half of the air space. The other pair ofantennas a₂₁and a₂₂ exhibit higher directionality in another half of theair space outside the terminal in back of the opposite associated backsurface, and the received and transmitted RF signal intensity patternexhibits higher intensity in the other half of the air space.Preferably, the antennas a₁₁ and a₁₂ and the antennas a₂₁and a₂₂ areplaced inside the terminal, and are not required to be exposed to theoutside. Since the two pairs of antennas of high directionality aredisposed as described above, the mobile wireless terminal 260 or 280 canreceive an RF signal radiated from an antenna of a reference node in anarbitrary direction, and can determine whether the incident directioncorresponds to the front side direction or the back side direction ofthe terminal, without considering the area arrangement.

The reference wireless stations 202, 222 and 242 of FIG. 2 may have thesame antenna arrangement as shown in FIG. 16 or 17. The referencewireless stations 202, 222 and 242 may have a pair of antennas of highdirectionality which are directed to the positioning areas 62 and 64, tothereby reduce the influence of multi-paths. When the size of theapparatus can be made larger, the reference wireless stations 202, 222and 242 may have two parallel rod antennas.

In the above description, it is assumed that the mobile wirelessterminals 260 to 282 and the reference wireless stations 200 to 242 aresubstantially on the same horizontal plane, and the vertical heightdifference between the antennas, and the inclinations of the antennareference lines of the terminals relative to the horizontal plane arenegligible or in the range of a tolerable error. The distances betweenthe reference wireless stations 200 to 242 are, for example, about 5 to10 m. The antennas of the reference wireless stations 200 to 242 have aheight in the range of, for example, about 1.5 to 2 m. The antennas ofthe mobile wireless terminals 260 to 282 have a height in the range of,for example, about 1 to 1.5 m. In this case, the accuracy or resolutionof the positioning of the terminal is expected to be within about 1 m.

However, when the height difference between the antennas, and theinclinations of the antenna reference lines are negligible, thedirection and the position are three-dimensionally corrected inaccordance with the known heights of the antennas of the referencewireless stations 200 to 242 and the known geography or contour of theareas, to thereby determine the position of each of the mobile wirelessterminals 260 to 282.

When RF signals received by the two antennas a₁ and a₂ are processed bythe communication node 400 of FIG. 4, the phase difference Δφ mayexhibit an error e due to the difference of the circuits of the paths inthe communication node 400. FIG. 18 shows an arrangement which includesa switch SW for switching connections between two antennas and two pathsfor correcting an error due to such a path difference.

First, the switch SW is placed on a first pole to provide an RF signalreceived via the antenna a₁ to a path 1 including the frequencyconverter 413 in FIG. 4, and provide an RF signal received via theantenna a₂ to a path 2 including the frequency converter 453. It isassumed that an output from the phase difference detector 415 exhibits aphase error e. Thus, the detected phase difference is Δφ+e. The switchSW is then placed on a second pole to provide an RF signal received viathe antenna a₁ to the path 2 including the frequency converter 453, andprovide an RF signal received via the antenna a₂ to the path 1 includingthe frequency converter 413. The detected phase difference is Δφ−e. Inorder to correct the error e, the subtraction is performed on the twophase differences to cancel the error e to obtain the result 2Δφ. Theresult is divided by two (2) to produce a corrected phase difference Δφ.

The above-described embodiments are only typical examples, and theirmodifications and variations are apparent to those skilled in the art.It should be noted that those skilled in the art can make variousmodifications to the above-described embodiments without departing fromthe principle of the invention and the accompanying claims.

1. A wireless apparatus for determining a phase difference of a receivedRF signal, comprising: first and second antennas displaced from eachother by a predetermined distance for receiving an RF signal; and anexclusive OR (EXOR) circuit comparing two binary signals derived fromthe received RF signal that are associated with said first and secondantennas respectively, wherein an absolute phase difference is based ona pulse width of the comparison.
 2. The apparatus according to claim 1,further comprising a detector for detecting source identificationincluded in said received RF signal.
 3. The apparatus according to claim1, wherein the apparatus is operable in accordance with a Bluetoothstandard.
 4. A method for determining a phase difference based onreceived RF signals associated with first and second antennasrespectively, comprising: producing a plurality of binary signals basedon the received RF signals; and exclusive ORing at least two of thebinary signals.
 5. The method according to claim 4, wherein theproducing the plurality of binary signals comprises: latching a firstsignal at a rising edge of a second signal; and comparing levels of thefirst and the second signals.